In recent years, light emitting diodes (hereinafter referred to as “LEDs”) emitting ultraviolet light having a wavelength from 200 to 400 nm are used for medical sterilization, sensors and the like. For example, LEDs having a substrate, a light-emitting chip mounted on the substrate surface, a support frame mounted around the light-emitting chip on the substrate and an optical member (such as a lens or a transparent pane) placed above the light emitting chip to close the opening of the support frame are known. The support frame and the optical member are usually bonded by an adhesive.
Optical members used for LEDs emitting ultraviolet light having a wavelength of at most 400 nm are required to be transparent and resistant to ultraviolet light having a wavelength of not more than 400 nm. Hence, quartz is usually used as the material for such optical members. However, quartz is shaped into lenses and the like by laser beam machining because injection molding of quartz is difficult due to its high glass transition temperature. Hence, production efficiency of quartz optical members is low. Therefore, some techniques were proposed for making lenses and other optical members from polymers having a fluorine-containing alicyclic structure (Patent Documents 1 and 2). Polymers having a fluorine-containing alicyclic structure melt at lower temperatures than quartz and, hence, are easily processed by melt molding and the like. They are highly transparent and resistant to ultraviolet light having a wavelength of 400 nm or less.
Polymers having a fluorine-containing alicyclic structure are proposed for use m adhesives for optical members, too.
For example, Patent Document 2 proposes use of a fluoropolymer which is a homopolymer selected from a specific group A or a copolymer selected from specific groups B, C and D, as a component of an adhesive composition.
In Patent Document 3, an adhesive containing a polymer obtained by cyclization polymerization of perfluoroallyl vinyl ether or perfluorobutenyl vinyl ether for bonding quartz lenses.